| Summary: | The reaction of UO<sub>2</sub> with the respective lanthanide metal and purified graphite in an arc-melting furnace led to the formation of solid solutions of the composition Ln<sub>x</sub>U<sub>1−x</sub>C<sub>2</sub>, with Ln = Tb, Dy, Ho, Tm, and Lu. They all crystallize in the tetragonal CaC<sub>2</sub> type structure (<i>I</i>4/<i>mmm</i>, <i>Z</i> = 2). Elemental analyses of selected samples (EDX) confirm that the composition of the resulting solid solution is in reasonable agreement with the nominal (weighed-in) composition of the starting materials, i.e., a significant evaporation of the lanthanide metals during the arc-melting synthesis does not occur. The lattice parameters of the solid solutions were extracted using <i>Le Bail</i> fits of high-resolution synchrotron powder diffraction data (beamline P02.1, DESY, Hamburg, Germany; beamline BL 09, DELTA, Dortmund, Germany), revealing ideal <i>Vegard</i> behavior for all five solid solutions. XANES investigations on all compounds at the Ln-<i>L<sub>III</sub></i> and U-<i>L<sub>III</sub></i> edges reveal that the occupancies of the U-6<i>d</i> orbitals decrease with increasing <i>x</i>, whereas the occupancies of the Ln-5<i>d</i> orbitals increase, pointing to an electron transfer from the uranium to the lanthanide cations. Examination of the shifts of the absorption edge (<i>E</i><sub>0</sub>) leads to the same finding.
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